Classes, fields, methods, constructors, and objects are the building blocks of object-based Java applications. This Java tutorial teaches you how to declare classes, describe attributes via fields ...

However, constructors and methods have important differences. If you are at all uncertain about this fundamental Java point, you should read this introductory-level tutorial.

I may return a GregorianFoo, or a JulianFoo. etc. etc. Constructors (in java), have no ability to do this. Though it's potentially something that could be added to the language.

In this example, the prepareByteArray method processes the Certificate object before passing it to the SuperClass constructor. With JEP 447, this process becomes more streamlined and intuitive.